The ice has been disappearing since 1984 because of global warming. This “perennial ice”—about double the thickness of seasonal ice—is the most critically important ice cover for the Arctic. It’s vital to the survival of native Arctic animals and people, of course, but it also plays a key role in moderating the entire planet’s climate. And there’s barely any of it left.
Check out Phil Plait’s Slate article from October for more.